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De-soldering Operation

Tools used for de-soldering projects

A source of heat is main requirement for de-soldering operation. That means that you must have a soldering iron or hot-air gun. Hot-air gun is the source of hot air and it is used mostly for de-soldering of surface-mount components. It is also good to have a de-soldering vacuum pump (solder sucker) to clean plated-through holes. For removing excess of solder in solder joint use de-soldering wick (de-soldering braid)
During de-soldering operation it is helpful to monitor changes of color and brightness in solder joint and adjust time of de-soldering work accordingly. If soldering iron does not start melting solder in couple seconds you should remove the soldering iron and then apply it to different point of solder joint. Apply soldering iron to place where iron tip has better contact with solder joint.

How to De-solder Components

Sometimes we have to replace a component on the circuit board if it does not work properly or it does not work at all. This process can damage circuit board or component.
Two main causes of damaging pads and conductors on circuit boards during a component removal are excessive heat and excessive pressure from soldering iron. Excessive heat from soldering iron or hot-air gun during component removal can even break component and lift pads and conductors on circuit board and make replacement of component more difficult.
Which de-soldering method we will use to remove components depends on what we are going to do – save the board only, save the component only, or save both the board and the component? If our plan is to do some repair on the printed circuit board then we will eventually find a broken component that should be replaced. Since the component is already broken (or does not work properly), we do not care much about are we going to damage it? However, we are very concern about damaging the board since we have to de-solder broken component and then insert and solder a new component in the same place. With proper method and tools it is possible to replace any component without damaging circuit board or component. Use the following rules when replacing components:

  • Make solder joint in less than 2 second
  • Finish de-soldering operation in less than 3 seconds. This time should be enough to melt solder in the joint.
  • Avoid excessive pressure on soldering iron during de-soldering operation since this can easily peel and break pads and conductors on circuit board. During de-soldering you should apply a light pressure with soldering iron (no more pressure than weight of soldering pencil).

One of the main factors that should be taken in consideration before de-soldering operation is thermal mass of joint. Soldering joint on single-sided circuit board has little thermal mass and therefore they require little heat. On other hand, soldering joint on double-sided board with plated-through hole has greater thermal mass and requires more heat. The total thermal mass of joint depends also of the number and size of conductors coming to joint. Thermal mass of joint is greater if more conductors coming to the solder joint. Thermal mass of joint is also greater if conductors have a bigger size. In addition, some components inserted in solder joint could have thick or long leads. This is additional thermal mass to solder joint. For solder joints with greater thermal mass we need soldering iron with higher wattage and bigger iron tip.